Thanks for checking out Bitmelo!
The editor doesn't support more than 1 palette, however you can swap the palette in game by using the bitmelo.screen.setPalette function. The palette has a max of 255 colors.
PNG exporting should be coming in the next update. PNG importing will be either in the next, or update after that as it's a bit more complicated.
A music tracker is the next big feature I want to add, but it may take a while as it's a pretty big undertaking.
Yea the github for the editor is where I'd prefer bug reports, but I should be able to see it either place.